Questions about stacking might

I've been trying a flamethrower/elixirs build recently and I have a few questions about the might boon.

I can test some of this for myself in the Mists when I get home from work, but anyways..
Do might duration bonuses stack? So if I have 2 rune of fires, 2 strengths, 2 Hoelbraks, does that total to +60%?
What exactly does might duration bonuses affect? I'm assuming when you give yourself the might boon through elixir b for sure but what about:

Flamethrower juggernaut trait?

HGH trait?

fire blast finishers?

I would also like to know what your opinions are on Deadly Mixture (+15% FT/EG damage) vs HGH (elixirs give 20 secs of might). 15% is a signficant bonus but I think doesn't affect condition damage, but might affects both so I was wondering if the damage is somewhat comparable? My build is pretty regularly tossing elixirs for cleansing formula in dungeons so it would affect allies too.
In Orr or whatever I would probably just take both, but I like to have cleansing formula in dungeons.

Combos use the stats of the character that finished the combo, so if you finish a fire field with a blast finisher everyone nearby gets longer lasting Might stacks however increased boon/might duration does nothing if another character finished the fire combo field.

I've never run a Engi, so cant comment on any of those specifics, but I run might stacking build on my Mesmer in PVP. I can say yes, your combination of runes is additive resulting in a 60% duration bonus for the Might boon.

Thanks everybody. I tried it and it seems boon duration does affect juggernaut and HGH trait.
Knowing that and runes stacking up to 60% I think I'll go with HGH. As Rouzeki says I think it suits how I play more anyways.

I use HGH with my condition damage/power build. Honestly, it's not that great. But depending on the build it fits well and if you build tanky you can get away with a bit more support. The problem is, you can't double it with Cleansing Formula as you already used that slot. If you throw elixirs only for the sole purpose of getting might they lose potential (AoE removing conditions three times is rather nice).

You can't stack might that high. I think durations indeed stack, the cap is still 100% though. With 50% boon duration you get 7 stacks of might with Juggernaut.

Elixir B is a different beast. The absurdly long might duration has been fixed with the last patch. In theory the cooldown is shorter than the might duration, so it should be possible to stack more and more might, right? It's not. I don't know where the numbers go wrong or if Elixir B is limited to one application only, but it just doesn't work.

Getting more than 10 stacks with the elixirs alone is hard. Everytime you switch weapons you lose one or two Juggernaut ticks. If you actually use different abilities, or heal yourself, you lose much more. 10 in average if you're lucky. Is that good? Yes. Are other classes better at getting might? By far. Before they nerfed elementalists it was easy to get 10 stacks on everyone and even more on yourself. It's still possible (although harder).

Before they nerfed elementalists it was easy to get 10 stacks on everyone and even more on yourself. It's still possible (although harder). With engineers you actually have to focus your build just to get the same amount of might.